This invention relates to a control device for an industrial machine comprising a numerical control device (hereinafter referred to as "an NC device" when applicable).
FIG. 1 shows the arrangement of a conventional control device comprising an NC device 10. In FIG. 1, reference numeral 1 designates a memory comprising a RAM, which stores programs and data; 2, a control section essentially including a CPU 2a, which controls the functions of the NC device in accordance with the system software loaded in the memory 1; 3, an arithmetic operation section for performing numerical operations under the control of the control section 2; 4, a tape reader for reading a paper tape in which an NC machining program (hereinafter referred to merely as "a machining program", when applicable) has been stored by perforation; 5, a program interface; 6, a feed shaft drive section including a servo amplifier etc.; 7, a feed shaft motor for driving a feed shaft; 8, a feed shaft encoder for outputting a feedback signal; and 9, an input/output signal interface provided for input signals which are used to start and stop the NC device, and for output signals such as NC device state signals and auxiliary function signals for controlling external equipment. Instead of the paper tape, a floppy disc may be employed.
Further in FIG. 1, reference numeral 20 designates a speed reducer; 21, a drive mechanism such as a ball screw; 22, a movable table of a machine, namely, a workpiece mounting stand; 26, a spindle unit; 27, a spindle motor; 28, a spindle amplifier for amplifying a spindle motor drive signal; 30, a gear unit for converting the speed of the spindle motor 27 into a value suitable for a tool 16; 31, a spindle head which holds the tool 16 and transmits the torque of the spindle motor 27 to the tool 16 through the gear unit 30; 32, spindle encoder coupled to the spindle head directly in a rate of 1:1, the spindle encoder 32 being a detector to which rotation of the tool 16 is transmitted as it is; and 33, a spindle encoder interface to apply the output of the spindle encoder 32 to the control section.
In machining a workpiece 15 with the above-described machine, the feed of the movable table 22 is synchronized with the rotation of the tool 16, which is a tapping tool in this case. In the case of FIG. 1, the workpiece 15 is moved, however, it goes without saying that, with the workpiece 15 held stationary, the spindle unit 26 may be moved by the feed shaft motor 7 while the tool 16 is being rotated.
In a tapping operation with the conventional control device, it is necessary to detect the speed of rotation of the tapping tool, and accordingly it is necessary to use the spindle encoder 32 to which the speed of rotation of the tapping tool is transmitted as it is.
On the other hand, in some of practical machines, because of the structure of the spindle unit, the spindle encoder 32 can not be suitably positioned as shown in FIG. 1. Such machines suffer from a difficulty that, for example, in the case of a single-threaded screw, it is difficult to feed the feed shaft one pitch with one revolution of the tapping tool.
In the case of a spindle unit in which the tapping tool is automatically replaced, the tapping tool is replaced by exchanging the spindle head 31 together with a part of the gear unit 30, i.e., together with one of the gears forming the gear unit 30. In this case, the spindle encoder 32 must be replaced together with the spindle head. Thus, the spindle unit is unavoidably intricate in structure.
Further, on the way of the machining operation under the control of the control device, when the machining operation is suspended due to an accident such as tool breakage, in order to start the machining operation again, the operator manually operates an operating panel (not shown) having a character and pattern display section and a keyboard. More specifically, various operations such as movement of the machine to a tool exchanging position, replacement of a tool, operation of a program restarting switch, search for a machining program, the setting of an M code, S code and T code, and movement of the shaft for restart and restoration are manually performed by the operator.
That is, with the conventional control device, the machining operation is restarted manually so that it takes a lot of time and labor to start the machining operation again if suspended.
Furthermore, the machining operation must be free from the accident that the movable table 22 is moved beyond the permitted range to break the machine or to interfere the workpiece with the tool. For this purpose, as shown in FIG. 2, limit switches 23 are provided. That is, when the movable table 22 is moved beyond the permitted range of movement, the limit switch 23 is activated to output a signal to stop the operation of the machine so that the movable range of the movable table 22 is limited.
With the conventional control device as described above, the range of movement of the movable table 22 is determined by the positions of the limit switches 23. Therefore, when it is required to change the range of movement, the limit switches 23 must be reinstalled. This will take a lot of time and labor.